1. Field of the Invention
This invention relates to a process for extruding tetrafluoroethylene/hexafluoropropylene copolymer.
2. Description of Related Art
U.S. Pat. No. 5,000,875 discloses the blending of thermally conductive fillers with fluorinated fluoropolymers to provide composites that exhibit surprisingly high thermal conductivity. The fluorination of the fluoropolymer involves exposing the fluoropolymer to fluorinating agent to convert unstable end groups to stable end groups. Unfortunately the addition of filler to the copolymer causes the viscosity of the resultant composition when melted to increase, resulting in a reduced production rate by typical melt fabrication processing such as extrusion, including injection molding. Tetrafluoroethylene (TFE)/hexafluoropropylene (HFP) copolymer is extruded at temperatures of at least 680° F. (360° C.), which is at least about 100° C. greater than the 260° C. melting temperature of the copolymer, and more typically at temperatures of at least 698° F. (370° C.). The increase in melt viscosity resulting from filler addition may be offset somewhat by increasing the melt temperature of the composition in the extrusion process. This, however, has the disadvantage of exposing the copolymer to degradation, causing discoloration and reduced physical properties of the extruded article.